"Those fish are stressed, there's a lot less water, there's no way of getting away from the fact that we're going to have more fish kills.

"You just have to think they're going to be bigger than last year."

Mr Smith agreed it was likely there would be even bigger fish kills coming, but said there would also be a huge number of deaths before then.

"If you do the count over the 100km of river, or 400km of river that there is at the moment that's battling, you're going to get a lot of fish that are going to die probably between now and summer," he said.

"It's going to be a slow burn, I'd call it. But it's definitely going to build."

"The extended dry conditions and diminishing flows within rivers presents significant risks for native fish populations throughout the Murray-Darling Basin," a spokeswoman for the NSW Department of Primary Industries (DPI) said.

"The record low levels of rain continue to pose risks for one of inland NSW's most productive recreational fisheries."

Preventative measures

The DPI said it was working with State Government agencies to look at what could be done to protect native fish populations and mitigate the risks as dry conditions continue.

"There's very little water left in the northern basin, but there would be other parts of New South Wales — say the Murrumbidgee Valley — where there may be some environmental water that could be used strategically to help maintain some flow in the river system," he said.

Debate about water policy

Professor Vertessy also believed the Murray-Darling Basin Plan was the best way forward.

"It was forged after a very long period of consultation, scientific analysis, and it's been gradually implemented, slower than we would like, but nonetheless it's already showing benefit," he said.